This invention relates to tools for gripping workpieces, and, more particularly, to a vacuum activated tool for grasping and picking up irregular pieces from a stack.
Increasing use of automation is a key to improving productivity in factory assembly operations. An important problem in the field of automation is the gripping, picking up, and moving of workpieces that are to be processed. For example, in automated electronics assembly operations it is necessary to grip and manipulate the circuit boards to which electronic devices and assemblies are attached. The motivation for the present invention is the need for a tool to pick up one, and only one, circuit board from a stack and then to move the board to an assembly location.
Printed circuit boards are thin, generally flat but often slightly warped, boards made of an electrically nonconducting material such as a resin. The circuit boards are available in a variety of thicknesses and lateral dimensions as needed for specific applications, but generally are about 0.030 to about 0.060 inches thick and of lateral dimensions of, for example, 2 inches by 4 inches to 6 inches by 10 inches. The boards are made of a polymeric resin that is slightly flexible, but can be cracked if tightly or irregularly gripped, as by a pliers.
The printed circuit boards are used to mount and interconnect the active and passive electronic components of an electronic system. For example, a number of integrated circuits, switches, resistors, capacitors, transformers, and the like, as required for any particular circuit, are mounted onto the board during the assembly operation. The components are connected with wires or conducting strips, and also connected to terminal strips that are usually provided at one end of the circuit board. The completed circuit boards are mounted in racks or holders in the electronic apparatus, and interconnected through the terminal strips. This modular approach makes possible the replacement of particular subsystems of a large, complex system by simply replacing one of the circuit boards.
The circuit boards are prepared by forming a sheet of the resin material and cutting it to the required size. Holes are punched or cut into the resin at the proper locations to mount the electronic components. Conducting strips and terminals strips are mounted on the board, and finally the components are added and interconnected.
Since much of the assembly work is repetitive in nature, robot devices have been developed to perform certain of the assembly functions such as placing the components onto the board and joining the components. Mechanical manipulators can be used to grasp and pick up the boards to move them between operations, but the use of mechanical manipulators for grasping the circuit boards has several drawbacks. The circuit boards are easily bent and cracked if they are grasped too tightly. If the circuit board has been preprinted with a metallic conductor pattern, the metal may be damaged or the pattern may be altered. Also, it is difficult for a mechanical robot hand to pick up just one thin circuit board from a stack. This problem is exacerbated when the stack of circuit boards includes boards of different sizes or orientations. Existing vacuum tools cannot be used to grasp the circuit boards, as the holes in the boards cause loss of vacuum and an inability to form a vacuum seal between the tool and the board.
No suitable approach has been proposed for grasping circuit boards, as to pick them up, one by one, from a stack, and for moving them to another location. A need therefore exists for such a tool, to permit further automation of the assembly operation. The present invention fulfills this need, and further provides related advantages.